The 13th is unlucky for some. And so it turned out for Michael Geoghegan. Summoned to dinner in the luxurious and graceful Goring hotel in the shadow of Buckingham Palace, the HSBC chief executive's 37-year globe-trotting career was about to come to a close.

His companion in the David Linley-designed dining room that Monday evening – 13 September – was another well-heeled banker. Sir Simon Robertson, a multimillionaire former Goldman Sachs partner, City grandee and most senior independent director on the HSBC board, needed to find a successor to Stephen Green, who was stepping down early as chairman, to join the coalition government.

Robertson – a super-smooth Old Etonian who was knighted in this year's birthday honours – was in a bit more of a hurry than he had expected to be. Back in March, he thought he had until the bank's 2011 annual meeting to find a successor for Green. But the chairman's decision to accept the post of trade minister left had Robertson with just a couple of weeks to resolve the situation.

One thing was clear as Robertson travelled to the Goring – the bank was not going to appoint the chief executive as its next chairman.

Geoghegan, who had joined HSBC at 19, might have believed the role was rightfully his, because that had been the tradition at the bank for most of the previous 150 years.

Robertson resolved to tell Geoghegan straight, over a bottle of fine wine, that his chosen candidate was Douglas Flint, the bank's finance director – and Geoghegan's subordinate. Geoghegan therefore had to decide whether he wanted to remain as chief executive to chairman Flint. It did not take him long to decide against.

The conversation at the Goring was meant to remain private until Wednesday, when an official announcement would be scheduled. But a series of leaks last week, claiming Geoghegan had threatened to resign if he was not given the top job, caused shockwaves across the City and sparked furious denials by the bank.

On Friday the bank convened an emergency board meeting, linking its 18 board members in Asia, Europe and the US by telephone. They rubberstamped Robertson's plan – installing Flint as chairman and replacing Geoghegan as chief executive with the ambitious but admired investment banker Stuart Gulliver – and the official announcement was released just minutes before the regulatory news services closed on Friday.

Flint will take over from Green on 3 December, while Gulliver will replace Geoghegan on New Year's Day. Geoghegan will not officially retire until March 2011 and will then be paid £200,000 as a consultant for an extra three months.

Recalling the dinner that ended his career at the "world's local bank", Geoghegan said: "I never really went out of my way to be chairman. You have to be asked, and the reality is I wasn't asked."

Geoghegan said that after the conversation with Robertson he came to a "very quick decision" that it was "time to hand over to the next generation". He told the bank the very next day, 14 September, that he intended to quit. This, he reckons, proves that he did not have a toddler-style temper tantrum by threatening to resign, potentially holding the board to ransom.

The City, which loves a good conspiracy theory, was this weekend still enthralled by the HSBC saga. Robertson, meanwhile, is trying to kill the image of a bank famed for its stability and clean succession-planning being rocked by internecine warfare. "It has been diabolical the way leaks have undermined certain individuals and what we're trying to do," he said.

Others considered for the chairman role included John Thornton, a former Goldman colleague and existing HSBC non-executive, along with international candidates.

If Geoghegan felt any bitterness as he participated in a series of conference calls from Singapore on Friday where he had been addressing banking supervisors, he was hiding it well. He described the pairing of Flint and Gulliver as an "awesome combination" and said: "Let's see the next team get on with it."

Geoghegan added that he'd had a "career that exceeded all my expectations". It has just not ended as smoothly as he would have hoped.